Vehicle transmission systems, cooling systems, and braking systems often use clutches or like devices to selectively transmit rotational forces from a drive shaft to an output member. Conventional clutch devices include an opposing pair of engagement surfaces that can be compelled toward or away from one another using an electrical, mechanical, pneumatic, or hydraulic actuation system. In general, the actuation system causes some relative axial shifting within the clutch device. Such axial movement is used to engage (or disengage) the opposing engagement surfaces, which rotationally interconnect (or rotationally disconnect) the drive shaft and the output member.
In general, the clutch can be operated to engage (or disengage) opposing clutch surfaces, which rotationally interconnect (or rotationally disconnect) the drive pulley and the output member. In an example related to fan clutches, when the clutch surfaces are shifted to the engaged position, the output member (carrying fan blades) is driven to rotate along with the drive pulley. However, when the clutch surfaces are shifted to the disengaged position, the output member is no longer directly urged by the drive pulley and may be free to stop rotating.
In clutch devices using pneumatic or hydraulic actuated systems, a piston may be acted upon by a set of springs to bias the piston toward one of the engaged or disengaged positions. Fluid pressure may act upon the piston, in a direction opposite to that of the spring force, to cause the piston portion to be axially shifted. Such axial movement is used to engage (or disengage) the opposing engagement surfaces, thus selectively controlling the rotation between the rotation between the drive shaft and the output member.
A viscous coupling includes a set of plates inside a sealed housing filled with a shearing fluid, where one set of plates is connected to an input rotating mechanism and the other set of plates is connected to an output mechanism. The shearing fluid, between the plates, causes drag between the slower set of plates (e.g., the output) and the faster set of plates (e.g., the input), providing torque transfer from the input mechanism to the output mechanism. The shearing fluid may be a heat-sensitive material, such as a silicone gel, that thickens and expands under heated conditions. Thus, when the shearing fluid “shears,” or churns, the fluid thickens and expands quickly to transfer substantial force between the input member and the output member.